1. Field of the Invention
This invention relates to organosiloxane compositions. More particularly, this invention relates to solubilized heat curable compositions comprising a vinyl-containing fluorosilicone gum, an organohydrogensiloxane curing agent for the composition, a platinum containing hydrosilation catalyst, a dispersed treated reinforcing silica filler, and an inert, volatile solvent. Evaporation of the solvent followed by heating of the composition results in formation of a cured elastomeric fluorosilicone film.
2. Description of the Prior Art
Dispersions and solutions containing organosiloxane compositions that cure by a hydrosilation reaction to yield elastomeric products are known in the art. U.S. Pat. No. 3,511,698, which issued to Talcott on May 12, 1970, describes a method for preparing an electrical insulator. In accordance with this method a resin base member is coated with a liquid dispersion that includes as the film forming material a polydiorganosiloxane wherein the repeating units are dimethylsiloxane and/or 3.3.3-trifluoropropylmethyl siloxane units in combination with a plurality of either vinyl groups or silicon bonded hydrogen atoms. The compositions also include a curing agent for the composition a platinum hydrosilation catalyst and an inert volatile liquid as the dispersing medium. The composition is heated to evaporate volatile materials and cure the composition to an elastomeric coating.
Talcott's compositions can optionally contain fillers such as aluminum oxide and silica, both of which are exemplified. Example 3 of this patent describes a coating composition wherein the polyorganosiloxane is a high viscosity fluid containing methyl-3,3,3-trifluoropropylsiloxane. dimethylsiloxane, methylhydrogensiloxane and dimethylhydrogensiloxy units. The composition includes a silica filler that had been previously treated with 2,4,6-trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane in the presence of ammonia.
The present inventor attempted to prepare coating compositions of the type described in the aforementioned Talcott patent by blending a fluorosilicone gum. a curing agent for the gum, a reinforcing silica filler. a number of different silica treating agents. including the cyclic siloxane exemplified by Talcott, and a platinum hydrosilation catalyst together with an organic liquid such as acetone that is a solvent for the gum. Of the silica treating agents evaluated only one type, a low molecular weight hydroxyl terminated poly(methyl-3,3,3-trifluoropropyl)siloxanes, yielded homogeneous compositions that were substantially free of agglomerated gel particles. These compositions are unique relative to those prepared using other silica treating agents in that they can be used as coating compositions without additional processing other than addition or removal of solvent to achieve the desired solids content.
An objective of this invention is to provide liquid. silica filled fluorosilicone coating compositions that cure by means of a platinum catalyzed hydrosilation reaction to yield elastomeric coatings. Other objectives will become apparent from the following specification and claims.